Cisco CCNA (200-301)Network AccessEasy
A network administrator is configuring a Cisco Catalyst switch to support multiple VLANs over a single link to another switch. The administrator intends to use 802.1Q tagging for VLAN identification. Which of the following commands correctly configures a port as an 802.1Q trunk?
- Aswitchport mode trunk
- Bswitchport port-security maximum 5
- Cswitchport mode access
- Dswitchport trunk encapsulation dot1q
Show answer & explanationAnswer & explanation
Correct answer: A. switchport mode trunk
The 'switchport mode trunk' command configures an interface as a permanent trunk link, which by default on modern Cisco switches uses 802.1Q encapsulation. Option C is often used for older switches or when explicitly changing encapsulation.
Why the other options are wrong
- B. This command configures port security, which is unrelated to trunking mode.
- C. Configures the port as an access port, allowing traffic for only one VLAN.
- D. This command explicitly sets the trunk encapsulation type, but 'switchport mode trunk' is the primary command to enable trunking. It's often used before 'switchport mode trunk' on older platforms that supported ISL, but is not strictly necessary on modern switches if 802.1Q is the only option.
802.1Q Trunk Configuration
To configure a switch port as an 802.1Q trunk, you use the 'switchport mode trunk' command, which enables the port to carry traffic for multiple VLANs.
- 802.1Q is the industry standard for VLAN tagging on trunk links.
- Trunk ports carry traffic for multiple VLANs, access ports carry traffic for a single VLAN.
- On modern Cisco switches, 802.1Q is the default and often only supported trunk encapsulation type.
Memory trick: Trunk Mode: Tagging Traffic for Transport